Comment by amanzi
Perhaps PlantUML isn't as new and interesting as Mermaid, but each time I try a side-by-side comparison, the results are always better in PlantUML than Mermaid. I'll admit that the Mermaid syntax is a lot easier to understand, but the PlantUML syntax is a lot more powerful. I especially like the new Activity diagrams in PlantUML with the conditionals and looping syntax.
Thats what I also found out, supported by llms, nice looking output. I have not found a proper left to right renderer for the activity diagrams